This invention relates to a magnetic recording and reproducing apparatus, and more particularly to a magnetic recording and reproducing apparatus which includes a magnetic head abrasion amount measuring instrument employing a magnetic sensor or a like element.
A magnetic head incorporated in a magnetic recording and reproducing apparatus is abraded as the time of use thereof proceeds because it contacts with a magnetic tape as a recording medium when it records and/or reproduces a signal. Particularly, where the magnetic head is of the rotary head type wherein it is mounted on a rotary drum, the magnetic head is abraded comparatively rapidly. The life of the rotary type magnetic head is rather short since the relative speed between the rotary type magnetic head and a magnetic tape used as a recording medium is higher than that of a stationary type magnetic head. As abrasion of a magnetic head proceeds, a region in which a magnetic head gap is formed, that is, a head depth, decreases, and the contacting characteristic with a magnetic tape and the electromagnetic conversion characteristic (frequency characteristics upon recording and reproduction) of the magnetic head vary significantly. Although it is possible to estimate these variations to some degree, since the amount of abrasive included in a tape is different depending upon the type of tape, if tapes of different types are used, it is difficult to accurately estimate the useful lifetime of the magnetic head. Therefore, in order to guarantee a magnetic reproduction characteristic of a magnetic recording and reproducing apparatus, the degree of abrasion of the magnetic head must be measured periodically to confirm that the degree of abrasion remains within an allowable range. For such measurement, an expensive jig for exclusive use has been prepared as a magnetic head abrasion measuring instrument. A operation is performed to open a housing of the magnetic recording and reproducing apparatus and set the jig in position relative to the rotary drum. However, such an operation requires much cost and time.
In order to solve the problem just described, the following patent applications regarding several magnetic head abrasion amount measuring instruments for measuring an abrasion amount of a magnetic head have been filed in Japan by the assignee of the present invention.
Japanese Patent Application No. Heisei 8-235471 discloses a magnetic head abrasion amount measuring instrument which includes a magnetic sensor disposed in an opposing relationship to but in a non-contacting relationship with a rotary magnetic head apparatus on which a magnetic head is mounted. The magnetic sensor is used as part of an oscillation element of an oscillation circuit. Further, taking note of the fact that the reluctance of a magnetic circuit at a position at which the magnetic head is opposed to the magnetic sensor varies depending upon the projecting amount of the magnetic head from the surface of the drum, a variation of the reluctance is taken as a variation of the oscillation frequency to measure the abrasion amount of the magnetic head.
Japanese Patent Application No. Heisei 7-353569 discloses another magnetic head abrasion amount measuring instrument wherein two magnetic sensors are disposed in an opposing relationship to a magnetic head such that they have different gaps from the magnetic head. The magnetic sensors are connected as variable oscillation elements to variable oscillation circuits such that, when the gaps of them from the drum are equal, same oscillation frequencies are outputted from the variable frequency circuits. The abrasion amount of the magnetic head is measured based on a variation of a difference between the oscillation frequencies of the magnetic sensors. Since a reluctance variation is involved in measurement of the head abrasion amount, the projecting amount of the head and hence the head abrasion amount can be measured with a high degree of accuracy. Since the measurement is performed without contact between the magnetic head and the magnetic sensors, there is no possibility that the magnetic head to be measured is damaged. Since the head abrasion amount is estimated making use of the difference between the two oscillation frequencies, the result of measurement is not influenced by a tolerance in shape or an allowance in mounting of the magnetic head.
Japanese Patent Application No. Heisei 7-285249 discloses a further magnetic head abrasion amount measuring instrument wherein a magnetic sensor is disposed in an opposing relationship to a magnetic head and in a non-contacting relationship with a magnetic tape. The magnetic sensor is used as part of an oscillation element of an oscillation circuit. Further, taking note of the fact that the reluctance of a magnetic circuit at a rotational position at which the magnetic head is opposed to the magnetic sensor varies depending upon the projecting amount of the magnetic head from the surface of the drum, a variation of the reluctance is taken as a variation of the oscillation frequency to measure the abrasion amount of the magnetic head. Since a reluctance variation is involved in measurement of the head abrasion amount, the projecting amount of the head and hence the head abrasion amount can be measured with a high degree of accuracy. Since the measurement is performed without contact between the magnetic head and the magnetic sensors, there is no possibility that the magnetic head to be measured is damaged. A temperature compensation apparatus is provided for the variable oscillation circuit so that the head abrasion amount can be measured without being influenced by an ambient temperature.
In the magnetic head abrasion amount measuring instruments described above, a pair of magnetic sensors are disposed at positions opposing a magnetic head mounted on a rotary drum outside an angular range within which a magnetic head is wrapped around the magnetic head, and a variation of the gap between the magnetic head and each of the magnetic sensors which is caused by abrasion of the magnetic head is converted into a variation in frequency making use of a variation in reluctance.
However, the proposals described above merely measure the abrasion amount of a magnetic head and output a result of the measurement as digital data, but do not explicitly propose a concrete mode or timing of a magnetic recording and reproducing apparatus in or at which the abrasion amount of the magnetic head is to be measured or a concrete display apparatus for allowing a user to visually perceive an abraded state or an abrasion amount of the magnetic head. Accordingly, the user cannot recognize the abraded state or the abrasion amount of the magnetic head, and this may possibly result in error in recording or reproduction.